1. Field of the Invention
This invention pertains to optical fiber connectors. More particularly, this invention pertains to means for connecting a plurality of optical fibers with means for switching optical couplings between the fibers.
2. Description of the Art
In the communications industry, the use of optical fibers for signal transmission is well known. While optical fibers present numerous advantages to conventional signal transmission, unique problems are associated with optical fiber transmission systems. For example, optical fibers having extremely small diameters require very precise alignment to avoid transmission and power losses. As a result, mechanical devices previously known in the prior art for terminating or switching conductors are not generally suitable for use with optical fibers.
To meet growing demand for optical fiber systems, the art has developed connectors and switches for use with optical fibers. An example of such a connector is described in a publication entitled "ST Series Multi-Mode Fiber Optic Connectors, Light Guide Apparatus Data Sheet," produced by AT&T Technologies, Inc. and bearing copyright date of 1985. The connector of the AT&T publication includes a ceramic plug which receives and retains an optical fiber. The plug is held in a flexible split-sleeve coupler. A similar plug with an optical fiber is inserted into the split-sleeve coupling with the sleeve holding the plugs in axial alignment and with the opposing fibers being optically coupled. The apparatus of the AT&T publication is not a switch per se in that it does not provide means for selectively changing optical couplings between choices of pairs of optical fibers.
An optical fiber switch is shown and described in a publication entitled "Electro-Optic Products `Moving Fiber` Switches Permit Greater System Predictability and Reliability" published by Siecor Corporation. The Siecor Switch shows lateral shifting of optic fibers.
Another example of an optical switch is shown in U.S. Pat. No. 4,033,669 to Hanson dated Jul. 5, 1977. In Hanson, a plurality of parallel rods retain and align a plurality of fibers. The fibers (such as elements 23, 25, and 27 in FIG. 3 of Hanson) are maintained in the interstice defined by opposing surfaces of rods (such as rods 24a-24e in FIG. 3 of Hanson). As more fully described in the text of the Hanson patent, alignment of certain rods and movement of the rods affects alignment and switching of the optical fibers.
Optical fiber switches are also shown and described in U.S. Pat. Nos. 4,245,885 and 4,229,068. Both patents are assigned to T.R.W., Inc. of Cleveland, Ohio, and show a structure where a plurality of rods define a plurality of interstitial channels into which optical fibers are placed.
In U.S. Pat. No. 4,245,885, optical fibers 24 are shown positioned within interstitial channels 76, 78, 80, 82, 84, and 86. In U.S. Pat. No. 4,229,068, the optical fibers are shown in FIG. 3 as items 93, 95, 97, 99, 101, 103, 105, and 107. The fibers are shown in the interstitial spaces defined between a common central rod 6 and a plurality of circumferential rods 91. An alternative embodiment is shown in FIG. 6 of U.S. Pat. No. 4,229,068 where the optical fibers 176 are provided within the interstitial channels defined between circumferential rods 174 and an outer sleeve 178. In U.S. Pat. Nos. 4,245,885 and 4,229,068, switching between optical fibers is accomplished by rotating the fiber arrays about a common axis.
Notwithstanding the aforesaid prior art couplers and switches, there is a continuing need for enhanced design of optical fiber couplers and switches. This need arises from the high cost associated with many prior art design. Optical fiber switches and couplers need to be mass produced in a manner which will have low manufacturing costs yet permit high performance of a finished product. Performance of optical switches is severely debilitated where a switch cannot align opposing optical fibers within prescribed tolerance limits. Also, it is desirable that a design will permit use of optic coupling enhancement techniques (such as use of index matching fluids) to improve optical performance.
The need for high tolerances in optical alignment is best understood with reference to the small dimensions involved in optical fibers. For example, a single mode optical fiber may have an outside diameter of 125 microns with an optic core having a diameter of about 10 microns.
In order to provide high performance optical coupling between opposing fibers, the cores of the fibers must be in opposing coaxial alignment with a high degree of tolerance. For example, where the axis of opposing optical fibers are offset by one micron, the one micron misalignment represents about 1 dB. In assessing the performance impact, 3 dB is approximately equivalent to a 50 percent power loss. It is generally recognized that misalignments in excess of 3 microns are not acceptable. Heretofore, switch designs which can meet this high degree of tolerance yet retain generally low manufacturing costs have been elusive.